Follow-up apparatus



Patented Jan. 9, 1951 FOLLOW-UP APPARATUS George N. Burkhart, Jr.,

to Duncan Electric La, Fayette,y Ind., assignor Manufacturing Company,

La Fayette, Ind., a corporation of Illinois Application February 8, 1947, Serial No. 727,421

4 Claims. (Cl. S18- 30) There are many situations in which it is desirable to drive a piece of apparatus accurately to a predetermined position from some other position on either side thereof and to control this drive by some element which is completely free of the load imposed on the driving motor. Quite often the position to which the apparatus is to be driven is varied more or less constantly either by manual control or by some form of automatic control.

For example, in various forms oi navigational equipment it lmay be desired to have some part of the equipment driven from one position to another depending on the speed or the compass course of a ship. Appreciable power may be required to drive this part of the equipment, but it is desirable not to derive this power from the usual speed or direction responsive devices of the ship since to do so would produce inaccuracies.

Accordingly, it is a practice in such instances to provide a driving motor for the apparatus which for convenience may be called a follow up motor, and to control this motor by some system which may be called a follow up system which senses any disturbance in the correct relationship between the driven apparatus and the device which it is to follow and causes the motor to drive the apparatus in one direction or the other. Thus it is possible to follow up accurately the speed or direction indications received from the usual ships instruments or such other indications as it may be desired to follow up in other types of I apparatus.

Accordingly to the present invention, a simplined and extremely dependable follow up system is provided. One feature of the invention is in the simplified control of the follow up motor, free from contacts which could cause contact trouble. According to this feature a motor which is constantly energized is controlled by sets of shading coils. one set for one direction of rotation and one for the other direction, each set being controlled by a saturable reactor. The saturable reactors in turn are controlled by vacuum tubes responsive to the indication being followed, with or without intermediate amplification.

Additional objects and advantages will be apparent from the following description and from the drawing which is a diagrammatic representation of a follow up system chosen for an illustration of the present invention.

Although the law requires a full and exact description of at least one form of the invention, such as that which follows. it is, of course, the purpose of a patent to cover each new inventive concept therein no matter how it may later be disguised by variations in form or additions of further improvements; and the appended claims are intended to accomplish this purpose by particularly pointing out the parts, improvements, or combinations in which the inventive concepts are found.

In the drawing the numeral II represents any instrument which is to be controlled by the follow up system of this invention. Ain the illustrated application of the invention, the position of the shaft i2 of the instrument is to be controlled in accordance with indications received over wires i3 which are the input wires to a control transformer i4. These input wires may come from a synchrogenerator i5, which might be connected to a ships navigational apparatus and may indicate the ships speed or its compass direction.

The control transformer i4 may be of any type. `One type which is at present preferred is the Bendix type 1CT. In this type of control transformer a voltage will be impressed on output Wires IB unless the shaft i2 is in exactly the position indicated by the indications received over wires i3. The instantaneous polarity of the voltage impressed on output wires I6 will depend upon the direction which shaft i2 is displaced from its correct position.

A follow-up motor i8 provided for driving the shaft I2 to its correct position. This motor is provided with a rotor I9 which in the illustrated `form drives a worm gear 2I, which in turn drives a worm wheel 22. In practice, the rotor i9 may more often be connected to shaft I2 by spur gears so as to have less backlash and power loss. The instrument I I to be controlled will also be driven by motor I8, being driven in the illustrated form by the same shaft I2 The present invention is concerned with controlling a motor such as the motor I8 in response to the voltages applied to output wires I6 by the control transformer I4, or by any other control device.

According to the present invention, voltages on wires I6 are applied to the control grid of the input tube 25 of an amplifier. The preferred circuit and constants of the amplifier are shown in the drawing and, hence, need not be described in detail. The two parts of tube 26 are connected in parallel. A single type tube such as 6J5 could be used but the twin type is preferred for greater dependability and so that both tubes will be of the same type.

The output of the input stage is applied through `the short circuiting of the shading coils.

a capacitance coupling to the control grids 38 of the output tube 28.

With weaker inputs another stage of amplication might be desired. With the apparatus indicated, however, it has been found desirable to cut down the input with resistance 40.

The two plate circuits of tube 28 are energized with opposite polarity by secondary coil v29 of power transformer 3| energized, by the same source which energizes synchro-generator I and control transformer I4. In other words, the center tap of the secondary coil 29 is connected to both cathddes of tube 28, but plate 34 is energized from one end of coil 29 while plate 36 is energized from the other end. The grids 30 may be suitably. biased by a secondary coil 32 on transformer 3l operating through a rectifier 33.

Plate 34 is connected with saturable reactor 4I while plate 36 is connected to saturable reactor 42, in each instance the connection being through one of the saturating coils 43. Since these coils are in the plate circuits of tube 28, the current through them will be uni-directional. The impulses therein due to the alternating. impressed voltage are largely leveled out /by the condensers 44.

The reactance coils 46 on the saturable reactors 4I and 42 are connected in series with shading coils on the motor I8. Thus the reactance coils 46 of saturable reactor 42 are connected across shading coils 48, which areconnected in the circuit in series. Likewise reactance coils 46 of the other saturable reactor 4I are connected across shading coils 49 of motor I8, these coils being connected in their circuit in series.

- As is well known in motors of this type a short circuiting of the shading coils 48 will cause the rotor I9 to rotate in one direction, assuming the main eld coil 5I is energized, while the short circuiting of the shading coils 49 will cause the rotor I9 to rotate in the opposite direction. In eiect, the saturable reactors 4I and 42 control When the current flows through a saturating coil 43 the high permeability of the core 52 is largely used up or saturated so that the core can have little eiect in oppsing the now of current through reactance coils 46. Hence the shading coils in series with these particular reactance coils are approximately shortA circuited. On the other hand, when saturating coil 43 carries relatively little current the core 52 greatly increases the reactance of coils 46 so that they oppose or retard the ow of current through the shading coils connected therewith.

With no voltage impressed on the wires I6 the voltage dividing resistance 35 will be adjusted so that conditions in the two reactors 4I and 42 are balanced and hence the various shading coils will have the current flow balanced therethrough so that the rotor I9.will not be driven. When a voltage is impressed on wires I6 by the control transformer I4, it will produce a change in the voltage impressed on grids 30. The direction of this change at any instant will depend upon the polarity of the voltage impressed on wires I6. With proper designing of the circuit, however, the polarity of the change of voltage on grid 30 will be in phase with the voltage on the voltage on one of the plate circuits and 180 out of phase with the other plate circuit.

.Because of the opposite polarity of the plate circuits of the tube 28, the current in one will be increased while the current in the other is decreased. Thus one of the saturable reactors will become less saturated and the other more saturated so that one pair of shading coils 48 or 48 will have a much heavier ow of current therethrough than the other pair of shading coils. This will cause the motor to rotate in one direction or the other depending upon which shading coils have the heavier flow of current.

Rotation of rotor I9 will continue until it has driven the shaft I'I to a position required by the indications received over wires I3 at which time the voltage will no longer be applied to wires `Iii and the balanced conditions of thereactors and the shading coils will be restored and the motor will stop. The'instrument I I to be controlled Will have been driven in proportion to the rotation of shaft I'I and, hence, will accurately correspond to the position required by the indications received over wires I3.

The follow-up motor I8 may be of a variety of types. At present, it is preferred, when small loads are'to be driven, to use Barber-Coleman reversible midget induction, motor eYAZ-3313 v. 60 cycle 50 R.. P. M. Y

It will be understood that similar follow-up systems can be used with other types of control. For example, a metal iiag carried by a delicate indicating instrument could be positioned between two high frequency oscillating coils connected to an amplifying circuit somewhat similar to that illustrated and mounted to be moved by the follow-up system, so as to follow the indicator accurately as it moved toward one coil or the other, some appropriate controlled device moving with the coils.

The term follow-up is not intended to be limited to literal interpretation. For example, the system may be controlled by a fluctuating voltage and an oilsetting adjustable voltage source driven by the follow-up motor to balance out the iiuctuating voltage.

In all such forms of the invention it will be apparent that a very simple and dependable follow-up system has been provided. The followup motor I8 is controlled without any contact, thus eliminating contact trouble. Control circuits for this motor do not need to be capable of handling its main power since they only handle the power induced in the shading coils. In spite of the simplicity and dependability, the apparatus is highly accurate.

I claim:

1. The combination of a reversible motor having an energizing coil and having shading coils for each direction of rotation, and saturable reactors; the shading coils for each direction of rotation being connected in series with reactance coils of a saturable reactor, and means for varying the saturation of the saturable reactors to provide greater current flow in the shading coils for one direction or the other, including electronic tube units having grids jointly energized under control of a control circuit, and plates, and plate circuits of opposite phase, correlated to the phase of the control circuit, and including saturating coils on the saturable reactors energized independently of the shading coils, said control circuit including contact-free means controlled by said motor for selectively energizing said grids in accordance with the direction of departure of a member controlled by said motor for its correct position.

2. The combination of a reversible motor .having an energizing coil and having shading coils for each direction of rotation, and saturable reactors; the shading coils for each direction of rotation being connected in series with reactance coils of a saturable reactor, and means for varyingr the saturation of the saturable reactors to provide greater current ilow in the shading coils for one direction or the other, including electronic tube units having grids jointly energized under control of a control circuit, and plates, and plate circuits of opposite phase, correlated to the phase of the control circuit, and including saturating coils on the saturable reactors energized independently of the shading coils, said control circuit including the secondary Winding of a rotary control transformer positioned by said motor, the primary of the control transformer r being energized with a shifting neutral axis by the device to be followed.

3, A follow-up system including a receiving rotary transformer having a rotary primary adapted to be energized by a rotary sender, and a secondary, a reversible motor for controlling the rotor including an energizing coil and a pair of shading coils directionally controlling the motor operation by the relative current intensity therein, and a control amplifier including an input circuit responsive to the transformer secondary coil, a pair of output plate circuits differentially controlled by the input circuit and energized by the ampliiier and a saturable reactor for each output circuit including a core. a saturating coil thereon connected in the associated output circuit, and coils on each core in circuit with one oi the shading coils of the motor.

4. A follow-up system including a receiving rotary transformer having a rotary primary adapted to be energized by a rotary sender, and a secondary, a reversible motor for controlling the rotor including an energizing coil and a pair of secondary coils directionally controlling the motor operation by the relative current intensity therein, and a control ampliiier including an input circuit responsive to the transformer secondary coil, a pair of output circuits differentially controlled by the input circuit and energized by the amplier, a saturable reactor for each output circuit including a core, a saturatng coil thereon connected in the associated output circuit, and coils on each core in circuit with one of the secondary coils of the motor, and a capacitor connected in each output circuit in parallel with the saturating coil to reduce the pulsations through the saturating coll.

GEORGE N. BURKHART, JR.

REFERENCES CITED The following references are of record in the 

